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Re: [TCML] New 833C VTTC - poor performance
You are right, I misunderstood. The grid voltage and current measurements would be taken at the feedback coil, correct? What would be the best way to take this measurement?
--- On Fri, 8/1/08, Quarkster <quarkster@xxxxxxx> wrote:
> From: Quarkster <quarkster@xxxxxxx>
> Subject: Re: [TCML] New 833C VTTC - poor performance
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Friday, August 1, 2008, 10:01 PM
> Kris -
>
> It sounds like there may be some confusion regarding
> filament voltage and grid drive current.
>
> DC Cox questioned your grid drive current, but you
> responded with some details about your filament transformer.
> These are totally different issues.
>
> Measure your filament voltage directly at the tube socket
> pins. If it's 10 volts, +/- 4 tenths of a volt, then the
> filament current will be automatically be OK at ~10A.
> Remember to pre-heat the filament for at least 30 seconds
> BEFORE you apply plate voltage, and also to measure filament
> voltage when the plate supply is turned on. Both filament
> and plate transformers in parallel may cause the AC line
> voltage to sag, especially if you are powering the coil
> through any sort of extension cord.
>
> It would also be interesting to measure the grid voltage
> and drive current. Typical 833A grid voltage is -150 volts,
> typical grid current is 70-90ma.
>
> Regards,
> Herr Zapp
>
>
> Kris Grillo <kristianisawesome@xxxxxxxxx> wrote:
> D.C., list,
>
> "check to be sure the TDK tank cap is rated for RF
> current and is not a DC
> filter type cap."
>
> As Garry mentioned, it is not specifically stated in the
> spec sheet, but it seems implied. Besides, this is the same
> capacitor that Steve used on his 833 coil and had much
> better success than I am having.
>
> "you may also have to experiment with the position of
> the grid leak coil --- sometimes it is necessary to have it
> 6-10" up the sec coil for best
> results."
>
> I have already done this. It is at about 9" up the
> secondary.
>
> "measure your grid drive current to be sure you are
> driving the 833 properly."
>
> This may be the problem. I am having nothing but problems
> with this "homebrew" filament transformer. I am
> without a means to test the current at the moment. I would
> assume it is at at least 10A. It is a 1200V MOT with the
> secondary and shunts removed. New secondary wound with 12
> gauge for 10 volts out. It must be eating up some power,
> judging by its temperature after about 10 minutes, but could
> it be enough to bring the current down below 10A?
>
>
>
>
>
>
>
> --- On Fri, 8/1/08, DC Cox wrote:
> From: DC Cox
> Subject: Re: [TCML] New 833C VTTC - poor performance
> To: "Tesla Coil Mailing List"
> Date: Friday, August 1, 2008, 2:23 PM
>
> check to be sure the TDK tank cap is rated for RF current
> and is not a DC
> filter type cap.
>
> you may also have to experiment with the position of the
> grid leak coil ---
> sometimes it is necessary to have it 6-10" up the sec
> coil for best
> results.
>
> measure your grid drive current to be sure you are driving
> the 833 properly.
>
> Dr. Resonance
>
>
>
>
> On Fri, Aug 1, 2008 at 12:05 PM, Kris Grillo
> wrote:
>
> > I just finished my first VTTC. It's a single 833C
> closely following
> Steve
> > Ward's single 833A schematic. The specs:
> > Secondary - 3.5" x 17" x #26
> > Topload - 2" x 7.5" toroid, about .25"
> above the top turn.
> > Primary - 29 turns #12 THHN on a 6.25" green
> pipe. Bottom turn level
> with
> > secondary bottom turn.
> > Filament supply - rewound mot, 10V even (does get
> warm).
> > Plate supply - very large (physically) old mot, shunts
> removed, voltage
> > doubler 2.05uf, mo diode, 2nf10kv ceramic disk
> > Tank cap - 2nf 40kV TDK UHV doorknob
> > Plate filter - 12 turns #12 on 50ohm 20W
> > Feedback coil - 20 turns #26
> > Grid leak - 4k 125w variable, 2nf 40kV TDK UHV
> doorknob
> > Everything is wired with #12 wire. All connections are
> tight.
> > No staccato yet
> >
> > For some reason, I can't get past 6" -
> 8" arks and about 75
> volts in from
> > the variac without the plate starting to glow orange.
> I've tried 24 -
> 20
> > turns on the feedback, 20 - 31 turns on the primary,
> varying the grid leak
> > resistance between 1K - 4K, varying the feedback coil
> from .5" above
> the
> > primary all the way to 8" above. I tried going
> with 1.75uf and 2uf on
> the
> > votage doubler. I tried a 4" pvc secondary with
> 19.75" of #26. I
> know the
> > 833C can do better than 8" arcs. It's a brand
> new Taylor from RF
> parts, by
> > the way.
> >
> > I'm out of ideas. Anyone have any suggestions?
> >
> > Thanks
> > Kris
> >
> >
> >
> >
> > _______________________________________________
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> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
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